A Croatian Agronomist’s Guide to Olive Tree Pruning

Garden shears play a sig­nif­i­cant role in deter­min­ing the yield and qual­ity of the olive har­vest, accord­ing to the well-known Croatian agron­o­mist Marijan Tomac.

As a result, when and how the olive trees are pruned is of the utmost impor­tance for qual­ity.

More than six mil­lion olive trees grow in Dalmatia and Istria. The best time to begin prun­ing is the sec­ond half of March or the begin­ning of April.

At this moment, farm­ers can dif­fer­en­ti­ate the fruit-bear­ing flower buds from the tree buds, which are the start of a new branch.

Previous to the arrival of the buds – from February to the begin­ning of March – Tomac rec­om­mends that farm­ers do not begin prun­ing as the olive tree reacts neg­a­tively to any­thing that dis­turbs its dor­mancy.

Pruning too early may lead to the loss of leaves, from which the tree absorbs sun­light and trans­forms it into energy. This is cru­cial for the devel­op­ment of flow­er­ing buds.

In addi­tion, ear­lier prun­ing encour­ages veg­e­ta­tion, so pos­si­ble cold fronts, with tem­per­a­tures as low as –9 ºC in recent years, may freeze the buds and leave behind trees with­out fruit.

There are mul­ti­ple advan­tages to prun­ing at the right time, imme­di­ately after the bud opens.

At this moment, less pro­fes­sional olive grow­ers can esti­mate the num­ber of flow­ers and thus the poten­tial amount of fruit.

It is impor­tant that in the case of olives, unlike other types of fruit, it is impos­si­ble to dis­tin­guish the flower bud from the tree buds with the naked eye.

However, Tomac warns that prun­ing should not be done after the moment of full flow­er­ing. By this time, the tree has already expended a lot of energy and resources, which would be wasted by prun­ing too late.

Late prun­ing by itself does not harm the tree, but sig­nif­i­cantly reduces branches’ veg­e­ta­tive growth and annual growth.

Despite deter­min­ing the nec­es­sary moment to begin prun­ing, most olive grow­ers quickly under­stand how to prune effec­tively after a short demon­stra­tion.

Most peo­ple under­stand that the canopy should be thinned, opened from the mid­dle, so there is enough sun­light. The shoots also should be short­ened, and the trees should not be allowed to become too tall.

Unfortunately, there are still those who leave the canopy too dense. Many olive grow­ers cut side shoots but leave the ver­ti­cal ones. This increases the height of the canopy from year to year.

“All the branches in the shade will not bear fruit,” Tomac said. ​“In addi­tion, the dense canopy affects the devel­op­ment of pea­cock eye dis­ease, the devel­op­ment of mead and the set­tle­ment of the soot fun­gus.”

He reit­er­ates that olive trees can be pruned from the move­ment shoots begin to grow to full flow­er­ing. Therefore, prun­ing should not be rushed.

Olive grow­ers who are less accus­tomed to rec­og­niz­ing the types of shoots should start prun­ing as late as pos­si­ble. Then they will see which will flower or form new branches.

Therefore, grow­ers should pre­pare their shears, saws and fruit wax to coat large wounds and slowly begin work­ing in the olive groves.

Once they are pruned, the branches need to be removed from the olive groves to pre­vent pest infes­ta­tions. Then, they can be mulched or chopped to make com­post.

Josip Pavlica, the sec­re­tary of the Zadar County Olive Growers Association, said that in addi­tion to treat­ing the parts of the tree from which the branches have been cut using olive wax, a cop­per-based prepa­ra­tion to pre­vent pathogens, pri­mar­ily bac­te­ria that cause olive can­cer, from enter­ing the tree should also be applied.

Disinfection of the cut­ting tool is also essen­tial.

“As soon as we prune one tree, dis­in­fect the tool before mov­ing on to another,” Pavlica said.

He added that proper prun­ing must be mod­er­ate to cre­ate an opti­mal ratio of wood and flower buds. Doing so pre­serves the trees’ grow­ing shape, encour­ages the growth of native branches and leads to abun­dant yields of high-qual­ity fruit.

However, Tomac said that grow­ers who are unsure should prune any­ways and learn from trial and error.

“He who cuts an olive tree can make a mis­take, but he who does not cut an olive tree makes a big­ger mis­take,” he con­cluded.